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don.honabach(at)pcperfect
Guest

Posted: Mon Jun 26, 2006 4:05 am Post subject: Avionics Stack - Single Point Grounding...

I’m trying to wrap my mind around the single-point grounding system as described in the ‘Connection, in particular as it affects devices in the avionics stack.  

   

If I understand the core process, you go ahead and bring all power grounds for cockpit related equipment to a single termination point on the firewall (i.e. the fast tab ground plane). What I’m a bit confused about though is that a prior post mentioned that most avionics run an internal ground to their case. For metal planes using metal panels and metal mounts wouldn’t this result in a dual ground system (and as such potential result in ground loop issues)? If so, does this mean that I should go ahead and insulate items in the panel that might have a noticeable affect (radios, intercom, etc.) or ???  

   

(Thanks in advance for any help and guidance!)  

   

Thanks,  

Don

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Mon Jun 26, 2006 5:13 am Post subject: Avionics Stack - Single Point Grounding...

On Jun 26, 2006, at 8:02 AM, Don Honabach wrote:

 	  Quote: 	
		  

For metal planes using metal panels and metal mounts wouldn’t this result in a dual ground system (and as such potential result in ground loop issues)? If so, does this mean that I should go ahead and insulate items in the panel that might have a noticeable affect (radios, intercom, etc.) or ???

	
Go ahead and ground the cases of your avionics. The issue comes when you are doing signal grounds, mostly mic wiring. There you want to have a single ground point for sure and it should be at your audio panel or intercom.

 Brian Lloyd                         361 Catterline Waybrian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)

I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery

Mark Phillips in TN

Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN

Posted: Mon Jun 26, 2006 5:45 am Post subject: Avionics Stack - Single Point Grounding...

In a message dated 6/26/06 7:09:07 AM Central Daylight Time, don.honabach(at)pcperfect.com writes:

 

  	  Quote: 	
		  Iâ€™m trying to wrap my mind around the single-point grounding system as described in the â€˜Connection, in particular as it affects devices in the avionics stack. 	


 

 >>>>

 

 Some EE out there will undoubtedly correct me, but this is how I look at it:

 

 Electrons come screaming out of the battery up an interstate highway of copper wire to each device.  Once being tortured therein, they must return to the fold (battery).  Given the choice of a return Interstate highway of more copper, or "over the river & thru the woods (device chassis, screws, metal mashed to other metal etc.- just think HIGHER RESISTANCE than the highway) they will prefer the easier route- one that is just as easy going as coming.  When all electrons travel this way, they are happy electrons and are less likely to insidiously attack your ears as noyz!   

 

 (and yeah, I know about "holes" but let's KIS)

 

 Mark - purty darn quiet Z-11 RV-6A

 do not archive unless this adds something to the discussion or I case I'm just plain wrong!

_________________
From The PossumWorks...

FLYaDIVE(at)aol.com
Guest

Posted: Mon Jun 26, 2006 6:33 am Post subject: Avionics Stack - Single Point Grounding...

In a message dated 6/26/06 8:09:07 AM Eastern Daylight Time, 

don.honabach(at)pcperfect.com writes:



 	  Quote: 	
		   For metal planes using metal panels and

  metal mounts wouldn't this result in a dual ground system (and as such

  potential result in ground loop issues)? If so, does this mean that I

  should go ahead and insulate items in the panel that might have a

  noticeable affect (radios, intercom, etc.) or ???

  

   

  

  (Thanks in advance for any help and guidance!)

  

   

  

  Thanks,

  

  Don

==============================
	


Don:



You bring up one of my pet peeves ... GROUND LOOPS!



99.99% of the electrically involved do not understand ground loops.  Due to 

the Internet, rumors and BS spread at the speed of an electron.



A single point ground is a good thing.  We ARE talking about DC (Battery) 

circuits, right?  But we are also talking about PLANES.  And in Composition 

Planes you MUST bring your ground to where ever you need it.  In metal - aluminum 

planes there is the possibility of using the plane as a ground.  Just like they 

do with cars.  The problem is aluminum is a very poor electrical conductor 

and a very good developer of corrosion.



OK, here are the Questions and the Answers:

As you mentioned Radios can use their CASE as the GROUND conductor.  

Is that the way to go?  

A: NO! And below are the reasons



Is there a problem with that?  

A: YES - The radio is NOT a solid mechanical connection its movement makes 

for a POOR Ground.  When it moves it creates ware points on the case and tray 

which remove the anodizing which increase the chance of corrosion.  And in 

return a POORER Ground.



Will it create a Ground Loop?

A: Well, lets ask the question: What is a Ground Loop?

There are TWO different types of Ground Loops ... AC & DC.

AC is anything with an Alternating Current that has a Frequency (i.e.: AF - 

AUDIO and RF - Radio Frequencies. More on this later.

DC is Direct Current and does NOT have a frequency or a pulse, Your Planes 

Battery / Alternator System.

A ground Loop in a DC circuit happens when there is a Potential Difference 

between what should be Common Ground points.

Why are they NOT COMMON?

A: Because there is some form of resistance that causes the Potential 

Difference (I.e.: Corrosion or Long Runs of Ground wire of the WRONG SIZE.



Can I use a separate Ground?

A: HELL YES!  The issue is NOT how many grounds you have but the QUALITY of 

the grounds.

If you use a single point ground to say an aluminum firewall and the area 

under the Nut & Bolt ... You did use a Nut & Bolt?  ... Corrodes ALL of your 

grounds to that tie point are now at risk.  To this add a bit of voltage and the 

corrosion will increase.  If it IA an aluminum point the corrosion is Aluminum 

Oxide and Aluminum Oxide is pretty damn close to an insulator.



Should I use an ADDITIONAL separate Ground? 

A: What do you think after reading the above Q&A?  

The answer should be YES!  

Keeping the potential difference on the Ground side of the circuit as low and 

as uniform as possible should be your goal.  It will help in the operation of 

the equipment and eliminate failure points as well as NOISE.



Ok, now onto AC -  AF & RF 

The basic rule is very simple, learn it and don't forget it:

With an AF circuit you ONLY GROUND at the Source of the AF.

Lets consider intercoms.  99.99% of the noise problem is because someone, 

somewhere in the installation GROUNDED the SHIELD at BOTH ENDS of the run.  It 

should be grounded where?  At the Source ... At the Intercom.  NOT at the Mic or 

Phone jack.  

Now someone is going to say ... Mine is grounded at both ends and it works 

fine.  Take a close LQQK  I'd bet there are plastic mountings around the jacks.



Ok, now onto RF

The basic rule is very simple, learn it and don't forget it (where have you 

heard that before):

With an RF circuit you GROUND at BOTH ends.

Both the Source (Radio) and Load (Antenna).



Question:  What kind of a device is a STROBE?

A:  It is both an AF and RF device.

The major part of the strobe noise is in the AF range.  

Long runs of Power Lines to the Strobe and Flash Tube lines help to spread 

the noise around.  Because the expanding and collapsing fields of the strobe the 

enegery/noise can be transmitted just like an RF signal.  Transmitted into 

other wires and down power lines.  This is heard as noise in the headsets.

Question:  How do you lessen or eliminate this noise?

Answer: Since it is both AF & RF you have to experiment. Use Shielded wire 

for your power (B+) lines. Start by grounding at the source.  Leave some 

shielded ground free at the far end.  Use Tolroids (ferrite beads) on the Power and 

Flash Tube wires.  Give it a test ... Try grounding the free end shield.  Do 

Not run strobe lines parallel to other wires or antennas.

There are other tricks but these are the basics that handle most of the 

problems.



So, do I believe in Single Point Grounds?  Yes, a whole lot of them!

So, do I believe in DC Ground Loops?  Yes, ONLY if you have POOR GROUNDS! 

<<<---  Keyword - letter - being 'S' - GROUNDS



Barry

"Chop'd Liver"

johnwcox(at)pacificnw.com
Guest

Posted: Mon Jun 26, 2006 7:44 am Post subject: Avionics Stack - Single Point Grounding...

I am no EE but in A & P school they were quite clear that electrons come from the negative terminal.  That is why the positive is always connected first and the negative terminal is connected last.  The better the negative (Ground) path – “Path of least resistance” …. I know a straight line between two points.  The electrons will always chose the lazy way.  Still an important idea for high quality ground connections.  

   

John Cox - $00.02  

         

  

From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Fiveonepw(at)aol.com

 Sent: Monday, June 26, 2006 6:40 AM

 To: aeroelectric-list(at)matronics.com

 Subject: Re: AeroElectric-List: Avionics Stack - Single Point Grounding...  

  

   

In a message dated 6/26/06 7:09:07 AM Central Daylight Time, don.honabach(at)pcperfect.com writes:

 

 

   

I’m trying to wrap my mind around the single-point grounding system as described in the ‘Connection, in particular as it affects devices in the avionics stack.  



 

 >>>>

 

 Some EE out there will undoubtedly correct me, but this is how I look at it:

 

 Electrons come screaming out of the battery up an interstate highway of copper wire to each device.  Once being tortured therein, they must return to the fold (battery).  Given the choice of a return Interstate highway of more copper, or "over the river & thru the woods (device chassis, screws, metal mashed to other metal etc.- just think HIGHER RESISTANCE than the highway) they will prefer the easier route- one that is just as easy going as coming.  When all electrons travel this way, they are happy electrons and are less likely to insidiously attack your ears as noyz!   

 

 (and yeah, I know about "holes" but let's KIS)

 

 Mark - purty darn quiet Z-11 RV-6A

 do not archive unless this adds something to the discussion or I case I'm just plain wrong!

lhelming(at)sigecom.net
Guest

Posted: Mon Jun 26, 2006 10:57 am Post subject: Avionics Stack - Single Point Grounding...

I understand what you are saying John about  connecting the negative last.  I however do it that way because if  connecting the positive last, you could easily ground the positive to some part  of the plane when connecting the positive.  If the negative is connected  last as you suggest, touching the airframe while fastening the positive or  negative terminal does not cause sparks to fly.  Knowing what I know about  electronics, I still am not sure if the electrons flow from negative to positive  or the holes left by the jumping electrons.  Let the debate begin.   Larry in Indiana

 [quote]   ---

FLYaDIVE(at)aol.com
Guest

Posted: Mon Jun 26, 2006 1:09 pm Post subject: Avionics Stack - Single Point Grounding...

In a message dated 6/26/06 3:06:33 PM Eastern Daylight Time, 

lhelming(at)sigecom.net writes:



 	  Quote: 	
		   Knowing what I know about electronics, I still am not sure if the electrons 

 flow from negative to positive or the holes left by the jumping electrons.  

 Let the debate begin.  Larry in Indiana

===============================
	


Larry:



It does not matter which horse you use to cross the stream.  Just don't 

change horses mid stream.



Barry

"Chop'd Liver"

FLYaDIVE(at)aol.com
Guest

Posted: Mon Jun 26, 2006 1:09 pm Post subject: Avionics Stack - Single Point Grounding...

In a message dated 6/26/06 3:06:33 PM Eastern Daylight Time, 

lhelming(at)sigecom.net writes:



 	  Quote: 	
		   I am no EE but in A & P school they were quite clear that electrons come 

from 
	


 	  Quote: 	
		   the negative terminal.  That is why the positive is always connected first 

 and the negative terminal is connected last. 

=========================
	


John:



If that is what they are teaching then have them grab +500 Volts in the Right 

Hand and -500 Volts in the Left Hand and turn the switch ON.  

Plus 500 added to Negative 500 is ZERO and there will be no voltage flow.  

The instructor should live Right?



Barry

"Chop'd Liver"

FLYaDIVE(at)aol.com
Guest

Posted: Mon Jun 26, 2006 1:34 pm Post subject: Avionics Stack - Single Point Grounding...

In a message dated 6/26/06 8:09:07 AM Eastern Daylight Time, 

don.honabach(at)pcperfect.com writes:



 	  Quote: 	
		   For metal planes using metal panels and

  metal mounts wouldn't this result in a dual ground system (and as such

  potential result in ground loop issues)? If so, does this mean that I

  should go ahead and insulate items in the panel that might have a

  noticeable affect (radios, intercom, etc.) or ???

  

   

  

  (Thanks in advance for any help and guidance!)

  

   

  

  Thanks,

  

  Don

==============================
	


Don:



You bring up one of my pet peeves ... GROUND LOOPS!



99.99% of the electrically involved do not understand ground loops.  Due to 

the Internet, rumors and BS spread at the speed of an electron.



A single point ground is a good thing.  We ARE talking about DC (Battery) 

circuits, right?  But we are also talking about PLANES.  And in Composition 

Planes you MUST bring your ground to where ever you need it.  In metal - aluminum 

planes there is the possibility of using the plane as a ground.  Just like they 

do with cars.  The problem is aluminum is a very poor electrical conductor 

and a very good developer of corrosion.



OK, here are the Questions and the Answers:

As you mentioned Radios can use their CASE as the GROUND conductor.  

Is that the way to go?  

A: NO! And below are the reasons



Is there a problem with that?  

A: YES - The radio is NOT a solid mechanical connection its movement makes 

for a POOR Ground.  When it moves it creates ware points on the case and tray 

which remove the anodizing which increase the chance of corrosion.  And in 

return a POORER Ground.



Will it create a Ground Loop?

A: Well, lets ask the question: What is a Ground Loop?

There are TWO different types of Ground Loops ... AC & DC.

AC is anything with an Alternating Current that has a Frequency (i.e.: AF - 

AUDIO and RF - Radio Frequencies. More on this later.

DC is Direct Current and does NOT have a frequency or a pulse, Your Planes 

Battery / Alternator System.

A ground Loop in a DC circuit happens when there is a Potential Difference 

between what should be Common Ground points.

Why are they NOT COMMON?

A: Because there is some form of resistance that causes the Potential 

Difference (I.e.: Corrosion or Long Runs of Ground wire of the WRONG SIZE.



Can I use a separate Ground?

A: HELL YES!  The issue is NOT how many grounds you have but the QUALITY of 

the grounds.

If you use a single point ground to say an aluminum firewall and the area 

under the Nut & Bolt ... You did use a Nut & Bolt?  ... Corrodes ALL of your 

grounds to that tie point are now at risk.  To this add a bit of voltage and the 

corrosion will increase.  If it IA an aluminum point the corrosion is Aluminum 

Oxide and Aluminum Oxide is pretty damn close to an insulator.



Should I use an ADDITIONAL separate Ground? 

A: What do you think after reading the above Q&A?  

The answer should be YES!  

Keeping the potential difference on the Ground side of the circuit as low and 

as uniform as possible should be your goal.  It will help in the operation of 

the equipment and eliminate failure points as well as NOISE.



Ok, now onto AC -  AF & RF 

The basic rule is very simple, learn it and don't forget it:

With an AF circuit you ONLY GROUND at the Source of the AF.

Lets consider intercoms.  99.99% of the noise problem is because someone, 

somewhere in the installation GROUNDED the SHIELD at BOTH ENDS of the run.  It 

should be grounded where?  At the Source ... At the Intercom.  NOT at the Mic or 

Phone jack.  

Now someone is going to say ... Mine is grounded at both ends and it works 

fine.  Take a close LQQK  I'd bet there are plastic mountings around the jacks.



Ok, now onto RF

The basic rule is very simple, learn it and don't forget it (where have you 

heard that before):

With an RF circuit you GROUND at BOTH ends.

Both the Source (Radio) and Load (Antenna).



Question:  What kind of a device is a STROBE?

A:  It is both an AF and RF device.

The major part of the strobe noise is in the AF range.  

Long runs of Power Lines to the Strobe and Flash Tube lines help to spread 

the noise around.  Because the expanding and collapsing fields of the strobe the 

enegery/noise can be transmitted just like an RF signal.  Transmitted into 

other wires and down power lines.  This is heard as noise in the headsets.

Question:  How do you lessen or eliminate this noise?

Answer: Since it is both AF & RF you have to experiment. Use Shielded wire 

for your power (B+) lines. Start by grounding at the source.  Leave some 

shielded ground free at the far end.  Use Tolroids (ferrite beads) on the Power and 

Flash Tube wires.  Give it a test ... Try grounding the free end shield.  Do 

Not run strobe lines parallel to other wires or antennas.

There are other tricks but these are the basics that handle most of the 

problems.



So, do I believe in Single Point Grounds?  Yes, a whole lot of them!

So, do I believe in DC Ground Loops?  Yes, ONLY if you have POOR GROUNDS! 

<<<---  Keyword - letter - being 'S' - GROUNDS



Barry

"Chop'd Liver"

N1DeltaWhiskey(at)comcast
Guest

Posted: Mon Jun 26, 2006 3:38 pm Post subject: Avionics Stack - Single Point Grounding...

Disagree, to a point.  Positive should be connected before ground when we are talking  about energy sources (say battery).  Why?  To prevent a short  circuit.  If the ground is connected first, any contact by the  positive lead will send sparks flying.  If the positive is connected first,  one will be attaching the wire to a system generally at ground  potential.

  

 This goes to the point missing from the  comments below.  Namely that electrons move only when invited to do so,  either when being sucked by a higher voltage potential, or  when being pushed around by electromagnetic fields (going to stop there  before revealing my ignorance about chemical reactions, but think the voltage  potential is the driving force there).  Connecting the ground first will  provide a complete circuit path if the positive terminal is shorted against the  grounded environment generally present in the airframe environment.   Connecting the positive first will only result in a ground coming in contacted  with an intended grounded airframe at the same potential, hence negligible, if  any, sparks will fly.

  

 For energy loads (consumers), it really does  not, usually, make much difference electrically, though it could mechanically  (don't have a specific instance, just leaving the door open to avoid rebuttal on  the point).  Besides, you have deenergized the potential circuit before  doing this - right?

  

 Doug Windhorn

 [quote]   ---

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Mon Jun 26, 2006 5:14 pm Post subject: Avionics Stack - Single Point Grounding...

<sigh> This thread is MUCH harder than it needs to be.



The avionics trays should be grounded. If they are in an aluminum  

airplane with an aluminum instrument panel and the panel is bolted or  

riveted to the airframe somehow, your job is done. If you have some  

sort of nonconducting panel such that the avionics trays are  

insulated from the rest of the airframe, run a wire from your  

avionics tray(s) to your single-point ground.



And this has nothing to do with the power ground for the radios. Each  

radio has a ground or multiple ground pins on its connector. These  

should be connected to your single point ground independently of the  

chassis ground.



Audio grounds, e.g. headphone, mic, audio inputs, etc., should be  

isolated and go to a single point ground at the radios. Mic and  

headphone jacks should be insulated from the airframe and a ground  

lead from each jack run back to the radio stack where they will  

ground at the intercom (if you have an intercom), the audio panel (if  

you have an audio panel without an intercom), or the comm radio (if  

you have no intercom or audio panel).



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

gnolin(at)sbcglobal.net
Guest

Posted: Mon Jun 26, 2006 6:21 pm Post subject: Avionics Stack - Single Point Grounding...

Electricity flows on all paths inversely proportional to the resistance, i.e. the lower the resistance, the higher current flow.  

  Hank 



Doug Windhorn <N1DeltaWhiskey(at)comcast.net> wrote:

  [quote]    (at)font-face {   font-family: Tahoma;  }  (at)page Section1 {size: 8.5in 11.0in; margin: 1.0in 1.25in 1.0in 1.25in; }  P.MsoNormal {   FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman"  }  LI.MsoNormal {   FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman"  }  DIV.MsoNormal {   FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman"  }  A:link {   COLOR: blue; TEXT-DECORATION: underline  }  SPAN.MsoHyperlink {   COLOR: blue; TEXT-DECORATION: underline  }  A:visited {   COLOR: purple; TEXT-DECORATION: underline  }   SPAN.MsoHyperlinkFollowed {   COLOR: purple; TEXT-DECORATION: underline  }  SPAN.EmailStyle17 {   COLOR: navy; FONT-FAMILY: Arial  }  DIV.Section1 {   page: Section1  }      Disagree, to a point.  Positive should be connected before ground when we are talking about energy sources (say battery).  Why?  To prevent a short circuit.  If the ground is connected first, any contact by the positive lead will send sparks flying.  If the positive is connected first, one will be attaching the wire to a system generally at ground potential.

   

  This goes to the point missing from the comments below.  Namely that electrons move only when invited to do so, either when being sucked by a higher voltage potential, or when being pushed around by electromagnetic fields (going to  stop there before revealing my ignorance about chemical reactions, but think the voltage potential is the driving force there).  Connecting the ground first will provide a complete circuit path if the positive terminal is shorted against the grounded environment generally present in the airframe environment.  Connecting the positive first will only result in a ground coming in contacted with an intended grounded airframe at the same potential, hence negligible, if any, sparks will fly.

   

  For energy loads (consumers), it really does not, usually, make much difference electrically, though it could mechanically (don't have a specific instance, just leaving the door open to avoid rebuttal on the point).  Besides, you have deenergized the potential circuit before doing this - right?

   

  Doug Windhorn

  [quote]  ---

don.honabach(at)pcperfect
Guest

Posted: Mon Jun 26, 2006 6:33 pm Post subject: Avionics Stack - Single Point Grounding...

Thanks everyone - lots of great information!



I understand from the comments I've received that 



1.  Grounding the 'power grounds' of the avionics to a firewall single-point system is a good thing.

 

2.  The fact that the avionics have a second power ground available to them via their cases to the plane's core structure (assuming metal panel/plane) is ok to leave as is, and putting in a single-point ground system 'on-top' of this 'poorer' case ground path is preferred.



Onward I go so one day I can go upwards...

 

Don



--

rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Mon Jun 26, 2006 11:03 pm Post subject: Avionics Stack - Single Point Grounding...

 	  Quote: 	
		   The avionics trays should be grounded. If they are in an aluminum 

 airplane with an aluminum instrument panel and the panel is bolted or 

 riveted to the airframe somehow, your job is done. If you have some sort 

 of nonconducting panel such that the avionics trays are insulated from 

 the rest of the airframe, run a wire from your avionics tray(s) to your 

 single-point ground.

 

 And this has nothing to do with the power ground for the radios. Each 

 radio has a ground or multiple ground pins on its connector. These 

 should be connected to your single point ground independently of the 

 chassis ground.


	


My intercom (Flightcom 403) has a ground pin and the case is grounded,

and there is continuity between the two.  I have not tested any of my

other avionics.  I wonder if this is common, or will cause a problem.



-- 

Mickey Coggins

http://www.rv8.ch/

#82007 finishing

do not archive

_________________
Mickey Coggins
http://www.rv8.ch/

FLYaDIVE(at)aol.com
Guest

Posted: Tue Jun 27, 2006 3:30 am Post subject: Avionics Stack - Single Point Grounding...

In a message dated 6/27/06 3:09:01 AM Eastern Daylight Time, 

mick-matronics(at)rv8.ch writes:



 	  Quote: 	
		   My intercom (Flightcom 403) has a ground pin and the case is grounded,

  and there is continuity between the two.  I have not tested any of my

  other avionics.  I wonder if this is common, or will cause a problem.

  

  -- 

  Mickey Coggins

  http://www.rv8.ch/

  #82007 finishing

====================
	


Mickey:



This depends on if it is an Audio Ground or a Power Ground.  



Barry

"Chop'd Liver"

nghertner(at)verizon.net
Guest

Posted: Tue Jun 27, 2006 9:05 am Post subject: Avionics Stack - Single Point Grounding...

On 6/26/06 7:34 PM, "Doug Windhorn" <N1DeltaWhiskey(at)comcast.net> wrote:



[quote] Disagree, to a point.  Positive should be connected before ground when we are

 talking about energy sources (say battery).  Why?  To prevent a short circuit.

 If the ground is connected first, any contact by the positive lead will send

 sparks flying.  If the positive is connected first, one will be attaching the

 wire to a system generally at ground potential.

 

 This goes to the point missing from the comments below.  Namely that electrons

 move only when invited to do so, either when being sucked by a higher voltage

 potential, or when being pushed around by electromagnetic fields (going to

 stop there before revealing my ignorance about chemical reactions, but think

 the voltage potential is the driving force there).  Connecting the ground

 first will provide a complete circuit path if the positive terminal is shorted

 against the grounded environment generally present in the airframe

 environment.  Connecting the positive first will only result in a ground

 coming in contacted with an intended grounded airframe at the same potential,

 hence negligible, if any, sparks will fly.

 

 For energy loads (consumers), it really does not, usually, make much

 difference electrically, though it could mechanically (don't have a specific

 instance, just leaving the door open to avoid rebuttal on the point).

 Besides, you have deenergized the potential circuit before doing this - right?

 

 Doug Windhorn

 ---

brian

Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA

Posted: Tue Jun 27, 2006 1:19 pm Post subject: Avionics Stack - Single Point Grounding...

On Jun 27, 2006, at 2:56 AM, Mickey Coggins wrote:



 	  Quote: 	
		   

 matronics(at)rv8.ch>



> The avionics trays should be grounded. If they are in an aluminum  

> airplane with an aluminum instrument panel and the panel is bolted  

> or riveted to the airframe somehow, your job is done. If you have  

> some sort of nonconducting panel such that the avionics trays are  

> insulated from the rest of the airframe, run a wire from your  

> avionics tray(s) to your single-point ground.

> And this has nothing to do with the power ground for the radios.  

> Each radio has a ground or multiple ground pins on its connector.  

> These should be connected to your single point ground  

> independently of the chassis ground.



 My intercom (Flightcom 403) has a ground pin and the case is grounded,

 and there is continuity between the two.  I have not tested any of my

 other avionics.  I wonder if this is common, or will cause a problem.


	


It will not cause a problem. The manufacturer designed it that way.



Some devices may show a low resistance between case and ground pin  

(on the order of 10 ohms or so). They use a 10 ohm resistor to get  

the shielding while the resistance greatly reduces the current in any  

potential ground loop.



The bottom line is that, if it has a metal case the manufacturer  

expects the case to ground to the airframe through the panel, or at  

least there is a very good chance that it will. If they don't want  

the case grounded you will find something about that in the  

documentation and they will provide the wherewithal to insulate the  

case.



Brian Lloyd                         361 Catterline Way

brian-yak AT lloyd DOT com          Folsom, CA 95630

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry

rv8ch

Joined: 10 Jan 2006
Posts: 250
Location: Switzerland

Posted: Tue Jun 27, 2006 10:23 pm Post subject: Avionics Stack - Single Point Grounding...

Brian Lloyd wrote:

 	  Quote: 	
		   The bottom line is that, if it has a metal case the manufacturer expects 

 the case to ground to the airframe through the panel, or at least there 

 is a very good chance that it will. If they don't want the case grounded 

 you will find something about that in the documentation and they will 

 provide the wherewithal to insulate the case.


	


Thanks a lot for the info.



-- 

Mickey Coggins

http://www.rv8.ch/

#82007 finishing

do not archive

_________________
Mickey Coggins
http://www.rv8.ch/

Hopperdhh(at)aol.com
Guest

Posted: Wed Jun 28, 2006 8:19 am Post subject: Avionics Stack - Single Point Grounding...

 

  

  

 John,

  

 I think that you are doing the right thing for the wrong reason.  The  reason for connection the UNGROUNDED terminal of a battery first is that if you  short your wrench to ground, you won't melt your wrench down or set  something on fire or burn yourself, etc.

  

 When the UNGROUNDED terminal is connected, then connect the ground and if  you short your wrench to ground, nothing will happen either.

  

 If we used positive ground in our airplanes, I would suggest that you  connect the negative terminal first.

  

 It really doesn't matter if electrons or holes are considered  "current."  Ben (Franklin) guessed wrong and all the universities still  teach positive current flow.  Oh well!

  

 Dan Hopper (EE -- retired)

 RV-7A

  

 do not archive

  

  

 In a message dated 6/26/2006 11:47:21 A.M. Eastern Daylight Time,  johnwcox(at)pacificnw.com writes:

  	  Quote: 	
		     

I am no EE but in A    & P school they were quite clear that electrons come from the negative    terminal.  That is why the positive is always connected first and the    negative terminal is connected last.  The better the negative (Ground)    path â€“ â€œPath of least resistanceâ€ â€¦. I know a straight line between two    points.  The electrons will always chose the lazy way.  Still an    important idea for high quality ground connections.   

    

John Cox -    $00.02

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